1. Technical Field of the Invention
The present invention relates generally to digital cameras, and more particularly to a digital camera that has the ability to adjust the ISO sensitivity of its optical pickup.
2. Background Art
Film cameras can be loaded with various “speeds” of film, typically expressed in terms of the ISO of the film. Typically, slower film (with a lower ISO number) will offer better image capture and resolution, while faster film (with a higher ISO number) allows photography at higher shutter speeds (such as for action shots) or in lower light conditions, albeit at some sacrifice in image resolution or quality.
Digital cameras use charge-coupled devices (CCDs), CMOS pickups, or other suitable semiconductor devices to capture an optical image from a lens system and convert it into an electronic representation of that image. Many digital cameras offer the user the ability to manually set the “ISO” of the pickup device. At lower ISO settings, the pickup will generally produce a better quality image, but only with sufficient light (either in brightness or in shutter duration). At higher ISO settings, the pickup will work with faster shutter settings or lower ambient light conditions, but will typically produce a noisier and/or grainier image. If a low ISO setting is used in very low light conditions (caused by low ambient light, a not-yet-recharged flash, a fast shutter speed, a small iris aperture, etc.), a digital imaging pickup may capture an image file consisting primarily of pixel values clustered very near the zero point (e.g. black). On the other hand, if a high ISO setting is used in very high light conditions, the pickup may capture an image file consisting primarily of pixel values clustered very near the saturation point or maximum value (e.g. white). By manually setting the ISO setting appropriately, the user can, in effect, shift the clustering of the pixel values upward or downward in the range between zero and the maximum value (between black and white), to achieve a better image.
A few digital cameras, such as the Nikon Coolpix 990, have an “auto ISO” mode in which the camera sets the ISO based-solely, I believe-on the amount of available light.